Michael Herne is an agent with the Activity.
The group for whom he works really has no name officially. It is called the Activity by the people in it because they have to have something to call it but on the books it likely is just a sub-paragraph number. It originally had been called the Intelligence Support Activity" but it soon just got shortened. It is run by a man who is known as Alpha. He has a real name, of course, and Herne had an opportunity to learn it but it is of no importance because to the men who work for the Activity, he always will be Alpha. He tells Herne when they first meet that his group is officially "a clerical support company - one that doesn't do much clerical work".
He goes on to explain that in the aftermath of the Iran Hostage Rescue fiasco, it was decided that before any such major action, it was vital to have someone in the area doing vital reconnaissance. Prior to a mission by the Seals, Delta, and other Special Forces teams, a member of the Activity scopes out the region and provides legitimate facts about the lay of the land and what was waiting in the shadows.
As Alpha explains, the CIA and Homeland Security might claim to have up-to-the-minute intel but they were driven more by politics and wishful thinking than hard facts and wishes get people killed needlessly. So one man goes, alone and independent, and gets the truth. And is there if things start hitting the fan.
Herne became a member over time. He was planning to head to college and a professional football career afterwards followed by a life as a coach. Then his father lost his job and his hope and took his own life and Herne's extremely task master of a mother told him college was out and his life was set working in the same small city in the hills of New York State. Herne dreaded that kind of dead-end life and rebelled. He fled home and joined the Army. He sent a good deal of his pay home to help his family but he was at least out of that town.
Herne certainly did not aim towards membership in the Activity because like most people he did not know it existed. When he shows an incredible shooting ability and a self-reliance and dependability far better than most, he got noticed. And Alpha came to visit. Herne was told of the possibility of membership but only after years of work and proving himself. He would have to make the Rangers. Then he would have to make it to Delta and work there for a while to keep proving himself. Then he would be invited to join. Herne did all that.
When we first meet him, he has been a member for several years and decided that his time in the most elite of groups was ending. He took a new job with the State Department's Intelligence branch as an analyst. But Alpha knows where he is at all times. And Alpha is too smart to let a good agent get away.